What is the minimum suction pressure required for fire pumps to avoid the need for a compound pressure and vacuum gauge?

The minimum suction pressure required for fire pumps to avoid the need for a compound pressure and vacuum gauge is 5 psi. This threshold is important because it helps ensure that the pump operates effectively without drawing a vacuum on the suction side, which can lead to cavitation. Cavitation occurs when the pressure in the system falls too low, causing the formation of vapor bubbles that can damage the pump impeller and reduce its efficiency.

By maintaining a suction pressure of at least 5 psi, the system avoids the complications associated with measuring both pressure and vacuum, simplifying the monitoring and maintenance of the system. When the suction pressure is below this level, having a compound gauge becomes necessary to provide readings on both the pressure and potential vacuum, thereby enabling better oversight of the pump's operational status and preventing possible damage due to low suction conditions.

In firefighting applications, ensuring adequate suction pressure is crucial for reliable performance and safety, which is why this minimum requirement is set.